Population ecology of heteromastus filiformis (polychaeta: capitallidae)

Abstract

The age structure and numerical dynamics of two intertidal populations of Heteromastus filiformis were studied by monthly or twice-monthly sampling for over 2 years. Adults were sexually mature through the winter and spawned in early spring, probably at the end of their second year. Settlement of larvae, and juvenile growth and mortality were studied by placing cores of azoic sediment in the field for 9 to 14 day intervals. Larvae settled from the plankton in March or April at rates that differed between the two populations, and were up to 2000 m −2·d −1. Juvenile densities as high as 66 500 m −2 were measured. Juveniles grew rapidly after settlement, doubling in size in less than two months. Adults grew more slowly, and no growth occurred during winter. The mortality rate of juveniles was initially about 0.03 d −1, but declined exponentially with time to zero, with a half-life of about 46 d at the high-intertidal site, and 71 d at the mid-intertidal site. Adults had a mortality rate not significantly different from zero, except in spring when their density declined at a rate of about 0.006 d −1, after the spawning period. Caging experiments to test the effects of motile macro-epifaunal predators on mortality rates of juveniles showed no significant effects.